The regulation and metering of fluid flow is an essential step performed in industry. For example, different caustics and corrosive acids are utilized in the manufacture of various integrated circuit devices. It can be particularly important to know quantities of the different reagents transferred, and consequently, measuring and controlling flow rate accurately can be critical to the quality of a finished product.
To adequately control the metering rate of a particular fluid, a flow meter must be sensitive to manual rate adjustments. Rate adjustments are generally accomplished by altering the percentage opening or incremental opening of a valve member. It is preferred that the flow rate respond in a predictable and repeatable linear fashion as the manual flow adjustment valve is cycled over the full range of flow to be measured by the flow meter. It is desirable to have control over extremely small flow changes for process control and product yield. It is preferred that for each incremental opening of the manual valve controlling the fluid flow there is a linear proportional response in flow rate over the entire range of the flow meter. Thus, a full rotation of the valve handle should give approximately the same change in flow rate whether such full turn occurs at low flow rates or high flow rates over design range of the meter.
Additionally, because of the nature of the chemicals that are employed in industry, apparatus for controlling and metering the flow of such chemicals must be impervious to deformation and deterioration which might occur when the chemicals under pressure come in contact with the components of such systems. The safety hazards inherent in a system not impervious to deterioration will be apparent.
Accordingly, the need exists for a flow controller and meter which gives a predictable, repeatable, linear flow performance. The flow meter should be designed to give an equal proportional response to flow for an equal change in manual flow control valve position. This equal linear response or change in flow rate should be maintained over substantially the entire range of flow rates through the meter. Further, the flow meter should be designed to withstand corrosive and caustic environments.
The present invention addresses these needs as well as other problems associated with existing flow controllers and meters. The present invention also offers further advantages over the prior art and solves problems associated therewith.